Simplify the following expression: $p = \dfrac{1}{9a} + \dfrac{6}{7a}$
Explanation: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $9a$ and $7a$ $\lcm(9a, 7a) = 63a$ $ p = \dfrac{7}{7} \cdot \dfrac{1}{9a} + \dfrac{9}{9} \cdot \dfrac{6}{7a} $ $p = \dfrac{7}{63a} + \dfrac{54}{63a}$ $p = \dfrac{7 +54}{63a}$ $p = \dfrac{61}{63a}$